Ensure static library module maps are declared as [system]

This is to mirror our use of -isystem for header search paths, making it so that headers imported via <> have warnings supressed

lib/cocoapods/generator/module_map.rb

@@ -67,7 +67,7 @@ module Pod
       #
       def generate
         <<-MODULE_MAP.strip_heredoc
-#{module_specifier_prefix}module #{target.product_module_name} {
+#{module_specifier_prefix}module #{target.product_module_name}#{module_declaration_attributes} {
   #{headers.join("\n  ")}
 
   export *
@@ -88,6 +88,15 @@ module Pod
           ''
         end
       end
+
+      # The suffix attributes to `module`.
+      # Ensures that library module maps are treated as `system` modules,
+      # supressing warnings when imported, as is done for header imports given via `-isystem`.
+      #
+      def module_declaration_attributes
+        return '' if target.requires_frameworks?
+        ' [system]'
+      end
     end
   end
 end

lib/cocoapods/installer/xcode/pods_project_generator/pod_target_installer.rb

@@ -622,7 +622,7 @@ module Pod
             UI.message "- Copying module map file to #{UI.path(path)}" do
               contents = custom_module_map.read
               unless target.requires_frameworks?
-                contents.gsub!(/^(\s*)framework\s+module/, '\1module')
+                contents.gsub!(/^(\s*)framework\s+(module [^{}]){/, '\1\2 [system] {')
               end
               generator = Generator::Constant.new(contents)
               update_changed_file(generator, path)

spec/unit/generator/module_map_spec.rb

@@ -27,7 +27,7 @@ module Pod
       @pod_target.stubs(:requires_frameworks?).returns(false)
       @gen.save_as(path)
       path.read.should == <<-EOS.strip_heredoc
-        module BananaLib {
+        module BananaLib [system] {
           umbrella header "BananaLib-umbrella.h"
 
           export *